We all live within the same 24-hour window, so you’d think it wouldn’t matter when we sleep—as long as we sleep. But it turns out the clock on your bedside table may be shaping how active you are the next day.
I’ve had my fair share of late nights and early mornings. Some of my best memories live in those odd in-between hours.
And it’s not just the youthful “out all night” kind of fun.
I once wrote about an oddly wonderful experience on a sleepless night when I pulled on an old army T-shirt with a big “USA” on the front and headed out for a run at 4:45 a.m. in Washington, D.C. It was already a perfect 75°F, and the city felt like a secret club for the very awake: workers, runners, and a pair of young women clearly just wrapping up their night at the Washington Monument. One of them pointed at my shirt, then at the 56 American flags circling the monument, and shouted with genuine enthusiasm, “Don’t you just LOVE America?!”
There’s a time in life for those late-night/early-morning adventures—and a time for something else entirely.
A large new study in the Proceedings of the National Academy of Sciences (PNAS) suggests that, for adults, there’s a real advantage to going to bed earlier.
Researchers tracked the sleep and activity patterns of 19,963 adults using wrist-worn biomedical devices. In total, they analyzed 5,995,080 “person-nights” of data, which let them see how consistent bedtimes lined up with how much people moved.
The pattern they found was striking: the earlier people went to sleep, the more moderate-to-vigorous physical activity they got the next day.
- Adults who were usually in bed by 9 p.m. logged about 30 extra minutes of physical activity the following day compared with those who routinely went to bed at 1 a.m.
- Compared with people who typically went to bed around 11 p.m., the 9 p.m. crowd still managed about 15 more minutes of movement.
It’s one of those findings that both makes intuitive sense and still feels surprising when the numbers spell it out.
After all, we all operate under the same 24-hour limit. So why should it matter if someone sleeps midnight to 8 a.m. instead of 10 p.m. to 6 a.m.? You’d think you could just choose a different time slot to exercise—say, 4 p.m.—no matter when you went to bed.
But maybe not. The researchers also found that when habitual night owls intentionally shifted their bedtimes earlier, their physical activity increased.
That suggests it’s not that late sleepers are inherently less interested in exercise. Instead, our daily routines and societal schedules might simply be aligned in a way that rewards earlier bedtimes. When you go to sleep earlier, it may become easier to fit movement into your day—whether that’s a morning workout or more energy and flexibility later on.
It’s worth emphasizing something you probably already know: exercise is linked to almost every positive health outcome you can name.
One 2017 study, for example, looked at people who got high levels of physical activity—defined as 30 minutes of jogging for women or 40 minutes for men, five days a week. The researchers found these exercisers enjoyed what they called a “biologic aging advantage” of about nine years compared with less active peers.
Commenting on the newer bedtime study, lead author Dr. Josh Leota of the School of Psychological Sciences at Monash University in Australia noted that these findings have important public health implications. Instead of treating sleep and physical activity as separate goals, he suggested that health campaigns could encourage earlier bedtimes as a simple way to support more active lifestyles—recognizing how tightly these two behaviors are intertwined.
I’m personally curious about when the earlier-to-bed group got their exercise. Were they early risers, getting their workouts done before breakfast? Or did they start work earlier, wrap up earlier, and use the time after work to be active?
Whatever the specifics, the broader message is useful—especially for busy leaders trying to juggle work, family, friendships, fitness, and sleep in a single packed day.
Otherwise, as my Inc.com colleague Jessica Stillman once pointed out while quoting Randi Zuckerberg, you can wind up facing an uncomfortable reality: out of work, sleep, family, friends, and fitness… you may only get to “pick three.”
Sleep on that—preferably before 9 p.m.
